sched: Teach might_sleep() about preemptible RCU

In practice, it is harmless to voluntarily sleep in a
rcu_read_lock() section if we are running under preempt rcu, but
it is illegal if we build a kernel running non-preemptable rcu.

Currently, might_sleep() doesn't notice sleepable operations
under rcu_read_lock() sections if we are running under
preemptable rcu because preempt_count() is left untouched after
rcu_read_lock() in this case. But we want developers who test
their changes under such config to notice the "sleeping while
atomic" issues.

So we add rcu_read_lock_nesting to prempt_count() in
might_sleep() checks.

[ v2: Handle rcu-tiny ]
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1260991265-8451-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index c4ba9a78721e1f4130526255050a1ed7f888ca4b..96cc307ed9f4ef0c85ffdf7509ad107dd73f77f2 100644 (file)
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -101,4 +101,9 @@ static inline void exit_rcu(void)
 {
 }
 
+static inline int rcu_preempt_depth(void)
+{
+       return 0;
+}
+
 #endif /* __LINUX_RCUTINY_H */

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index c93eee5911b0760ab81ae3791a31c7c340f800eb..8044b1b9433381ebd77dfa11cf4838c37690facb 100644 (file)
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -45,6 +45,12 @@ extern void __rcu_read_unlock(void);
 extern void synchronize_rcu(void);
 extern void exit_rcu(void);
 
+/*
+ * Defined as macro as it is a very low level header
+ * included from areas that don't even know about current
+ */
+#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
+
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 static inline void __rcu_read_lock(void)
@@ -63,6 +69,11 @@ static inline void exit_rcu(void)
 {
 }
 
+static inline int rcu_preempt_depth(void)
+{
+       return 0;
+}
+
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 static inline void __rcu_read_lock_bh(void)

diff --git a/kernel/sched.c b/kernel/sched.c
index af7dfa74e6bbcbe604be3a7bc1b5c8bed8cc33a9..7be88a7be0471f8f7c90c6f8e5e795982e6d7aae 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9682,7 +9682,7 @@ void __init sched_init(void)
 #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
 static inline int preempt_count_equals(int preempt_offset)
 {
-       int nested = preempt_count() & ~PREEMPT_ACTIVE;
+       int nested = (preempt_count() & ~PREEMPT_ACTIVE) + rcu_preempt_depth();
 
        return (nested == PREEMPT_INATOMIC_BASE + preempt_offset);
 }